<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        /* 具体效果如下：

            ☆
            ☆☆
            ☆☆☆
            ☆☆☆☆
            ☆☆☆☆☆ */
            var sum = '';
            for(var i = 1; i <= 5; i++){
                for(var j = 1; j <= i; j++){
                    sum = sum + '☆';
                }
                sum = sum + '\n';
            }
            console.log(sum);
    </script>
</body>
</html>